A hot air balloon rises vertically upward at a constant velocity of 9,8 m.s-1, when a man throws one of the sandbags at a velocity of 9,8 m.s-1 downward. What is the relative starting velocity of the sandbag in regards to the earth?

The velocity of the sand bag relative to the earth is equal to the velocity of the balloon relative to the earth plus the velocity of the sand bag relative to the balloon. Remember that these velocities are vectors, so they have direction. Post back with what you get for an answer.